This invention relates to amplifiers and in particular, operational amplifiers including class AB amplifiers.
High-speed operational amplifiers (xe2x80x9cop-ampsxe2x80x9d) that are capable of accepting, amplifying and outputting signals with minimal distortion or noise caused by the amplifier itself, are desirable in analog circuits. There are different op-amp architectures that are suitable for high-speed applications in analog circuits. The two main circuit topologies for voltage feedback op-amps are the folded cascode op-amp and the class AB op-amp. The folded cascode op-amp offers low noise, low distortion, high gain, wide bandwidth and good DC performance, but poor slew rate performance. The class AB op-amp offers improved slew rate performance but poor noise and DC performance.
There is desired an improved op-amp that retains the advantages of these configurations and overcomes the disadvantages.
The present invention achieves technical advantages as a folded cascode op-amp using a hyperbolic cosine (xe2x80x9ccoshxe2x80x9d) comparator for the biasing of the transistors, thus transforming the relationship of output current with respect to differential voltage input from a hyperbolic tangent function (xe2x80x9ctanhxe2x80x9d) to a hyperbolic sine function (xe2x80x9csinhxe2x80x9d). In this manner, the folded cascode op-amp has slew rate characteristics similar to a class AB op-amp but with low noise, low distortion and better DC performance. The transformation makes the conventional folded cascode op-amp very fast without affecting its desirable parameters of low noise, low distortion, high gain, wide bandwidth and good DC performance.